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    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <script>
      // 原型对象的应用 扩展内置对象方法

      Array.prototype.sum = function () {
        for (var i = 0; i < this.length; i++) {
          sum += this[i];
        }
        return sum;
      };
      //   Array.prototype={
      //       sum:function(){
      //        var sum=0;
      //       for (var i = 0; i < this.length; i++) {
      //         sum += this[i];
      //       }
      //       return sum;
      //     }
      //       }

      var arr = [1, 2, 3];
      console.log(arr.sum());
      console.log(Array.prototype);
      var arr1 = new Array(11, 22, 33);
      console.log(arr1.sum());
    </script>
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